Many semiconductor devices include non-silicon work function materials. For example, metal-oxide semiconductor (MOS) devices may include a gate electrode that includes a metal to assist in setting the effective work function for the gate electrode. Use of metal-containing electrodes in such devices has become increasingly important as the feature size of the devices decreases. Although various processes for forming metal gate electrodes have been developed, many of these processes exhibit unacceptable feature-size dependent performance variations. As a result, as the feature sizes of semiconductor devices decrease, these processes become increasingly problematic.
For example, in some devices, the effective work function of a metal-containing gate electrode may be determined by averaging work functions exhibited by domains within the gate electrode film that may have different crystal orientations and/or morphological phases of the metal gate electrode material. In some settings, the size of these domains may vary according to film deposition conditions and/or film thickness. As a gate length becomes smaller in MOS devices, the domain size may occupy a relatively larger portion of gate electrode, potentially leading to domain-specific work function differences that may have a greater effect on the overall work function of the device. In turn, there may be gate-to-gate work function variation that depends on the gate feature size, which may result in poor device performance.
Metal gate electrodes may also be difficult to integrate into device manufacturing processes because it can be difficult to deposit metal gate electrode films having desired film uniformity or other properties. For example, some semiconductor devices may include a three-dimensional gate dielectric supporting structure, such as a fin extending from the substrate that supports gate dielectric material on one or more of surfaces of the fin, or a replacement gate structure including an opening formed in the substrate surface that supports gate dielectric material on one or more surfaces therein. Depositing thin films of metal gate electrode material on the sidewalls of such structures may be challenging when using some existing deposition processes approaches. For example, mass transport phenomena inherent in physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques may provide poor step coverage in such structures and may lead to inconsistent film thickness as a function of the gate dielectric supporting structure height.
Further, because some properties of a material that may make it attractive as a potential metal gate electrode material may not be present in a thermodynamically stable phase of the material, it may be difficult to form a desirable but less stable phase of the material using traditional PVD and CVD techniques. For example, a PVD deposition may lead to a film initially having identical composition as the target or targets, and the high energies involved in the PVD process may lead to equilibration into a more thermodynamically stable form of the material, which has less desirable work function properties. As another example, attempts to form desirable metastable phases of material with CVD processes may lead to incomplete conversion and within substrate compositional non-uniformities, potentially leading to downstream processing difficulties and/or device performance problems. Accordingly, improved phase-stabilized films and methods of forming the films are desired.